Methods for determining the concentration of serum constituents are indispensable for the diagnosis and treatment of clinical conditions. The volume of plasma must be known when quantitating the concentration of a serum constituent. The volume of red blood cells present in blood (hematocrit) in universally proportional to the volume of plasma. The hematocrit, however, varies significantly from person to person posing a problem when analyzing whole blood for plasma (serum) chemistries. The present invention describes an unexpected way of overcoming this difficulty. It is widely recognized that in otherwise healthy individuals, hematocrit is directly proportional to total hemoglobin. Hemoglobin determinations are more consistent and accurate than hematocrit determinations. Thus the present invention permits the measurement accurate calculation of the concentration of the serum constituent being measured from a dried blood sample.
Another object of the invention is to provide an assay for blood analytes such as cholesterol and prostate specific antigen (PSA) which obviates the need for a hematocrit determination.
These and other objects of the invention would be apparent in light of the detailed description below.